Method for the manufacture of titanium metal



METHOD FOR THE MANUFACTURE OF TITANIUM METAL Elbert C. Smith, Henderson, and Carl K. Stoddard, Las Vegas, Nev., assignors to Titanium Metals Corporation of America, New York, N.Y., a corporation of Pennsylvania Application December 1, 1955 Serial No. 550,471

7 Claims. 01. 7s s4;s

No Drawing.

This invention relates to the production of metallic titanium, and more particularly to improvements in the general process wherein titanium tetrachloride is reacted with a metallic reducing agent.

The general process to which this invention relates, involves instilling onto a molten reducing agent, for in-' stance, magnesium contained in a reactor under a protective gas and at substantially atmospheric pressure, sufiicient titanium tetrachloride to produce titanium metal as a result of its reduction by the reducing metal. This process is generally referred to as the Kroll process and is described in U.S. Patent No. 2,205,854. In commercial practice of the Kroll process, however, the efficiency of utilization of the magnesium reducing metal generally is not high. This efliciency may not exceed 6070% under ordinary conditions and rarely, if ever, reaches 80%. This occurs; apparently, because the titanium metal forms initially on the surface of the molten magnesium in the reactor, gradually bridging across to form a more or less densedeposit of titanium sponge. "Underneath the sponge there remains, however, considerable metallic magnesium, whichis not available for reaction with the titanium tetrachloride introduced to the reaction zone. The'low efiiciency .of magnesium utilization results in obvious lossaof this. raw material, and'also complicates the subsequent separation of the titanium sponge product from the excess magnesiumemployed and the magnesium chloride by-product. i

It is,.therefore, the principal object of this invention to provide an improved method for the production of metallic titanium. An additional object is toprovide a method for production of titanium metal from titanium tetrachloride by reduction with a reducing metal in which the utilization efliciency of the reducing metal is substantially improved. A still further object of this invention is to provide a more efficient method for production of titaniummetalby reaction of titanium tetrachloride and a reducing metal with respect to utilization of raw material and subsequent separation of the titanium sponge produced from excess reagents and by-products. These and other objects of this invention will beapparent from the following detailed description thereof. a V

This invention, in its broadest aspects, contemplates reduction of titanium tetrachloride with a reducing metal.

in a two-step process. Titanium tetrachloride is initially fed, in at or near the top of areaction zone through a.

reactor'wall or cover ontometallic magnesium until from 60-80% of the stoichiometric amount required toreact with the. magnesium present in the reactor has been added. Atthis. point the reaction generally slows down, as is evidenced by a pressure rise in the reaction zone caused.

by inability of the remaining magnesium metal to absorb and react ,with the added titanium tetrachloride. Instillation of titanium tetrachloride is, accordingto this invention, thereupon discontinued and titanium tetrachloride is then fed into .the reaction zone through an anhydrous halide salt .contain'edin asump or well at the bottom of the. reaction zone. ,The titanium tetrachloride atent added at this stage must be forcibly introduced to overcome the hydraulic head of the molten halide salt in the sump or well as well as to overcome any pressure building up in the reactor at this stage. Preferably the titanium tetrachloride is pumped into the reaction zone. However, it will be appreciated that an equivalent effect may be obtained by positive feeding from an elevated storage tank which provides sufiicient hydraulic pressure, or other means. Titanium tetrachloride is introduced into' the reaction zone as described through the sump or well until the total added, including that instilled originally, amounts to between 98% of the stoichiometric amount required to react with the magnesium in the reactor. This may be readily accomplished, according to the practice of this invention, since the introduction of titanium tetrachloride in the bottom of the reactor makes available for reduction the residual magnesium metal reducing agent heretofore rendered inaccessible by formation of titanium sponge as a dense covering crust. After the required amount of titanium tetrachloride has been added, the reactor and its contents are cooled and the titanium sponge formed therein is removed and separated from by-product contaminants according to well-known methods.

The reaction zone is maintained free from contaminating gases during reduction of TiCl for example, by provision the-rein of an atmosphere of argon or helium.

The reaction Zone in which the reduction takes place is contained by a suitable reactor pot which is characterized by provision of a sump or well in the bottom thereof. The sump may be of convenient dimensions, advantageously at least a few inches deep, and during the course of the reduction'is maintained full of an anhydrous molten halide; salt, preferably either magnesium chloride or a magnesium chloride-containing chloride salt mixture. Other halide salts may be used, selected from the group consisting of alkali and alkaline earth metal halides and mixtures thereof, which have a density greater than that of metallic magnesium; Preferably the halide salt or mixture should melt at a temperature below the melting point of magnesium metal. Magnesium chloride is convenient because'it is the by-product of the reaction and may be recovered without contamination with other materials. Its melting point, however, is slightly above that of magnesium metal, and is not therefore as good as mixtures of chloride salts having a melting point below that of magnesium. A mixture of magnesium and sodium or potas slum chloride containing about 50% magnesium chloride is particularly advantageous since this has a relatively low melting point and the presence of sodium or potassium chloride will not affect the recovery of metallic magnesium from the byproduct chlorides by electrolysis. The function'of the molten salt sump at the bottom of the reactor is to protect the titanium tetrachloride introduction means through the sump from plugging by precipitation of metallic titanium in the immediate vicinity thereof during the initial stages of the reaction. found that if the sump is not first filled with molten halide salt, and molten magnesium is allowed to collect therein, it is extremely difiicult to obtain an open feed through the'bottom titanium tetrachloride entry pipe because titanium metal will be produced by reaction with magnesium in the vicinity of the entry pipe and tends to clog the outflow. 1

In its physical aspects the sump should be more or less separated from the reaction zone but free communication between the sump and the reaction Zone is essential for ready passage of titanium tetrachloride. If desired, the sump may be constructed as an appendage to the reactor bottom, having an opening into the reaction zone, small by comparison to the reactor diameter, but of sufficient dimensions to permit adequate flow of titanium tetra- It has been chloride. In a preferred organization a false bottom plate is employed in the reactor, supported by legs or other convenient means an appropriate distance, which maybe several inches, above the actual bottom. The plate divides the reactor proper into the reaction zone above and the sump below. The plate is provided with perforations to permit ready passage of titanium tetra chloride, pumped into the sump during the second stage of the process, from the sump into the reaction zone above. If desired, the titanium feed pipe into the sump may be arranged to pass through the reaction zone into the sump through a hole in the false bottom plate so that its opening is in the sump below the salt level. This has the advantage that an additional titanium tetrachloride feed pipe through the reactor bottom is not required.

An empty reactor, prepared for use, is first charged with sufiicient anhydrous halide salt to fill the sump at the bottom. The required amount of metallic reducing agent is then charged to the reactor and the reactor closed. A protective or inert gas such as helium and argon is employed to flush out residual air from the reaction zone, and the reactor then closed and placed in a suitable furnace and heated by external means to a reaction temperature between 650 and 900 C. At this temperature the halide salt will become molten and fill the sump at the bottom of the reaction zone, and the metallic magnesium will also melt and float on the halide salt. In a preferred embodiment of the invention, wherein the halide salt has a lower meltingpoint than magnesium, thiswill melt first, filling the sump, and the magnesium melting subsequently will float thereon. This will more positively prevent the presence of magnesium at the bottom of the sump, as by adhesion to the walls, and will provide a cleaner input for submerged titanium tetrachloride introduction. Titanium tetrachloride instillation is then initiated; the titanium tetrachloride being introduced through the cover of the reactor in either liquid or gaseous form whereupon it reacts with the molten magnesium, which at this stage floats upon the molten halide salt in the bottom of the reactor. Titanium tetrachloride is added at a rate so that the temperature in the.

reactor does not exceed preferably 900 C., and in'order to prevent contamination by reaction with the reactor wall it should not be above 1000 C. The pressure in the reactor is an indication of the progress of the reaction. It will be found that after between 60% and 80% of the titanium tetrachloride theoretically required to react with the magnesium charge has been added the pressure in the reactor increases, indicating that insufficient magnesium metal is available to quickly absorb and react with the titanium tetrachloride being fed into the reaction zone. The slowing up of the reaction before all of the magnesium is utilized is apparently caused by formation of a crust of metallic titanium on the upper surface of the magnesium metal, which after a while hecomes more or less impermeable and the additional magnesium entrapped below this crust is not readily reached by the titanium tetrachloride being instilled on top of the previously formed metallic titanium. Most generally this occurs when between 60% and 80% of the theoretical amount of titanium tetrachloride has been introduced.

At this stage, feeding of titanium tetrachloride into the troducing means, enables the titanium tetrachloride to be readily introduced into the reaction zone during this latter introduction stage without plugging of the titanium tetrachloride entry pipe. The titanium tetrachloride fed during this stage is forcibly introduced rather than simply allowed to flow in as the titanium tetrachloride used in the first part of the reduction. During the bottom feeding sufiicient pressure must be maintained in the titanium tetrachloride supply to overcome the hydraulic head of the moltenhalide salt in the sump at the bottom of the reactor and also any pressure which may build up due to a somewhat slower absorption rate of the titanium tetrachlon'de by the residual metallic magnesium- Mechanical pumping means are preferably employed, although a supply tank arranged at a sufiicient elevation to provide the necessary hydraulic head may alternatively be used. The amount of titanium tetrachloride added in the second stage through the bottom of the reaction zone should be sufiicient when combined with that added during the first stage, to provide between and 98% of the titanium tetrachloride needed to react with all of the magnesium metal in the reactor to produce metallic titanium therefrom. It is best not to attempt to introduce more than 98%, and preferably not more than since the distribution of any reagents in the reaction zone is never perfect, and attempts to obtain utilization efliciency too close to 100% may often result in the formation of lower chlorides of titanium which are pyrophorio and may result in loss of product when the reactor is finally opened.

- After completion of the reduction reaction, the reactor and its contents, still protected from atmospheric contamination, are cooled and the contents removed and excess magnesium and by-product magnesium chloride are separated by known methods. They may involve a leaching operation in which the bored out chips are treated with a dilute acid solution, or a vacuum distillation where the contaminants are evolved under the influence of heat and extremely low pressure.

It is significant that the titanium metal sponge product :produced by this process will contain a substantially smaller amount of residual excess reducing metal than has been obtainable by heretofore known methods. As a result separation of the titanium metal product from excess reducing metal and by-product reducing metal chloride becomes much more simplified and eflicient.

Magnesium chloride by-product may be drained from the reaction pot during the course of the reaction. This procedure removes a bulk of by-product from the reaction zones and provides additional space for deposition of metallic titanium. When draining magnesium chloride in the process of this invention, however, care should be taken that the halide salt content of the well or sump at the bottom of the pot is not removed. This may be readily arranged by providing the drainage tap hole above the normal level of the halide salt in the sump.

The following example illustrates the practice of the process of this invention.

Example I interior flushed and filled with helium. The reactor pot was then placed in a gas-fired furnace and heated to 800 C., at which temperature the halide salt was molten and filled the sump, and the metallic magnesium was alsomolten floating on its surface in the bottom of the reac-,

tion zone, that is, generally above the falsebottom plate.

Titanium tetrachloride was then introduced into the pot. through the top feed pipe, the pipe leading into the sump The rate of TiCL,

being closed oflf by a suitable valve.

introduction was such that the heat'generated by the reac- .tin didnot raisethe temperature of the pot and its con- .tents above 900 C. After four hours, 693 pounds of TiCL; had been introduced corresponding to 79.3% of the amount theoretically required to react with all the origi nallyscharged magnesium .to produce metallic titanium. .At this point the-reaction slowed down and additional 'TiCL, fed into the top of the pot did not readily react {with themagnesium as indicated by a pressure rise inside ;the pot. Feeding TiCl at the top was thereforediscontinued and the feed pipe leading into the top of the reaction zone was closed by a valve.

The TiCl feed pipe leading into the sump was then employed to feed additional TiCL, into the reaction zone, through the halide salt in the sump and the-perforations in the false bottom plate. A pump was employed having a capacity for pumping TiCl against pressures up to lbs. per square inch, although the actual pressures encountei'ed were substantially less than this, and a positive forcefulintroducti on of Tic-l was thereby obtained. 'One'hundred and forty-three pounds of TiCl were introduced in this'fashion over a period of 1% hours. The TiCl feed was then shut off since the total added amounted to 95.7% of that required theoretically to react with .the magnesium charged. After moltenmagnesium chloride 'was drained, the pot was cooled to room temperature and the titanium sponge bored out. The borings contained only 4.7% unused metallic magnesium and 43% magnesium chloride. The pure titanium metalwas readily separated from the magnesium and magnesium chloride by leaching with a hydrochloric acid solution.

The efliciency of utilization of magnesium in this run was over 95% and the titanium metal was of good quality, having a Brinell hardness number of 125.

We claim:

1. A method for producing titanium metal which comprises; charging to a reaction zone suflicient anhydrous salt selected from the group consisting of alkali and alkaline earth metal chlorides and mixtures thereof having a density greater than that of metallic magnesium, to fill, when molten, a sump in the bottom of said zone, charging metallic magnesium into said zone, heating to melt said salt and said metallic magnesium thereby forming molten metallic magnesium floating on the surface of molten salt in said sump, instilling on top of said molten metallic magnesium between 60% and 80% of the titanium tetrachloride theoretically required to react with said metallic magnesium to produce titanium metal in the form of sponge in said reaction zone above said sump, and subsequently forcefully introducing through the molten salt in said sump additional titanium tetrachloride to react with metallic magnesium entrapped in said sponge, by contact from the underside thereof, the total amount of titanium tetrachloride added being between 90% and 98% of that theoretically required to react with said charged metallic magnesium to produce titanium metal, meanwhile maintaining said reaction zone free from contaminating gases.

2. A method for producing titanium metal which comprises; charging to a reaction zone suificient anhydrous magnesium chloride salt to fill, when molten, a sump in the bottom of said zone, charging metallic magnesium into said zone, heating to melt said salt and said metallic magnesium thereby forming molten metallic magnesium floating on the surface of molten salt in said sump, instilling on top of said molten metallic magnesium between 60% and 80% of the titanium tetrachloride theoretically required to react with said metallic magnesium to produce titanium metal in the form of sponge in said reaction zone above said sump, and subsequently forcefully introducing through the molten salt in said sump additional titanium tetrachloride to react with metallic magnesium entrapped in said sponge, by contact from the underside thereof, the total amount of titanium tetrachloride added being between 90% and 98% of that theoretically required to react with said'charged metallic magnesium to produce titanium metal, meanwhilemaintaining said reaction zone free from contaminating gases.

3. A method for producing titanium metal Which comprises; charging to a reactionzone sufficient anhydrous salt composed of a mixture of magnesium and sodium chlorides having a density greater than that of metallic magnesium, to fill, when molten, a sumpin the bottom of said zone, charging metallic magnesium into said zone, heating to melt said salt and said metallic magnesium thereby forming molten metallic magnesium floating on the surface of molten salt in said sump, instilling on top of said molten metallic magnesium between 60% "and of the titanium tetrachloride theoretically required to react with said metallic magnesium to produce titanium metal in the form of sponge in said reaction zone above said sump, and subsequently forcefully introducing through the molten salt in said sump'additional titanium tetrachloride to react with metallic magnesium entrapped in said sponge, by contact from the underside thereof, the total amount of titanium tetrachloride added being be- .tween and 98% of that theoretically required to react with said charged metallic magnesium to produce titanium metal,-meanwhile maintaining said reaction zone free from contaminating gases.

4.'A method for producing titaniummetal which comprises; charging to a reaction zone-suflicient anhydrous salt composed of amixture of about 50% magnesium chloride and about 50% sodium chloride, to fill, when molten, a sumpin the bottom of said zone,-charging metallic magnesium into said zone, heating to melt said salt and said metallic magnesium thereby forming molten metallic magnesium floating on the surface of molten salt in said sump, instilling on top of said molten metallic magnesium between 60% and 80% of the titanium tetrachloride theoretically required to react with said metallic magnesium to produce titanium metal in the form of sponge in said reaction zone above said sump, and subsequently forcefully introducing through the molten salt in said sump additional titanium tetrachloride to react with metallic magnesium entrapped in said sponge, by contact from the underside thereof, the total amount of titanium tetrachloride added being between 90% and 98% of that theoretically required toreact with said charged metallic magnesium to produce titanium metal, meanwhile maintaining said reaction zone free from contaminating gases.

5. A method for producing titanium metal which comprises; charging to a reaction zone suflicient anhydrous salt selected from the group consisting of alkali and alkaline earth metal chlorides and mixtures thereof having a density greater than that of metallic magnesium, to fill, when molten, a sump formed by a perforated false bottom plate in the bottom of said zone, charging metallic magnesium into said zone, heating to melt said salt and said metallic magnesium thereby forming molten metallic magnesium floating on the surface of molten salt in said sump, instilling on top of said molten metallic magnesium between 60% and 80% of the titanium tetrachloride theoretically required to react with said metallic magnesium to produce titanium metal in the form of sponge in said reaction zone above said sump, and subsequently forcefully introducing through the molten salt in said sump additional titanium tetrachloride to react with metallic magnesium entrapped in said sponge, by contact from the underside thereof, the total amount of titanium tetrachloride added being between 90% and 98% of that theoretically required to react with said charged metallic magnesium to produce titanium metal, meanwhile maintaining said reaction zone free from contaminating gases.

6. A method for producing titanium metal which comprises; charging to a reaction zone sufficient anhydrous salt selected fiom the group consisting of alkali and alkaline earth metal chlorides and mixtures thereof having a density greater than that of metallic magnesium, to

'fill, when molten, a sump formed as an appendage to the bottom of said zone, charging metallic'magnesium into said zone, heating to melt said salt and said metallic magnesiumthereby forming molten metallic magnesium floating on the surface of moltensalt in said sump, in-

stilling on top of said molten metallic magnesium between 60% and 80% of the titanium tetrachloride theoretically required to react with said metallic magnesium to produce titanium metal in the form of sponge in said reaction zone above said sump, and subsequently forcefully introducing through the molten salt in said sump additional titanium tetrachloride to react with metallic magnesium entrapped in said sponge, by contact from the underside thereof, the total amount of titanium tetrachloride added being between 90% and 98% of' that theoretically required to react with said charged metallic magnesium to produce titanium metal, meanwhile maintaining said reaction zone free from con taminating gases.

'7. A method for producing'titanium'metal whichcomprises; charging to a reaction zone sufiicient anhydrous I salt selected from the group consisting of alkali and alkaline earth-metal chlorides and mixtures thereof having a density greater than that of metallic magnesium, to fill, when molten, a sump in the bottom of said zone, chargingmetallic magnesium into said zone, heating to melt said salt and said metallic magnesium thereby forming molten metallic magnesium floating on the surface of molten salt in'said sump, instilling on top ofsaid molten metallic magnesium between 60% and 80% ofithe'tijtanium tetrachloride theoretically required, to react with said metallic:v magnesium to produce titanium metal in 'the fornrof sponge in said reaction zone above said 1 sump, andsubsequently pumping through the molten salt ,in said sump additional titanium tetrachloride to react with metallic magnesium entrapped in saidfsponge, by

contact from the underside thereof, the, total amount of titanium tetrachloride addedbeing between 90% and 98% of that theoretically required to react withv said charged metallic magnesium to produce titanium metal, meanwhile maintaining said reaction; zone free'frorn contaminatinggases. g

References Cited in thefile of this patent UNITEDv STATES'PATENTS OTHER REFERENCES Websters New International Dictionary, 2nd ed,, un-

labridgeiapage' 1703,p ublished'in 1940by G. and C.

Merriam Co., Springfield, Mass. Y

Metal Industry, May 16, 1947, page 363. 

1. A METHOD FOR PRODUCING TITANIUM METAL WHICH COMPRISES; CHARGING TO A REACTION ZONE SUFFICIENT ANHYDROUS SALT SELECTED FROM THE GROUP CONSISTING ALKALI AND ALKALINE EARTH METAL CHLORIDES AND MIXTURES THEREOF HAVING A DENSITY GREATER THAN THAT OF METALLIC MAGNESIUM, TO FILL, WHEN MOLTEN, A SUMP IN THE BOTTOM OF SAID ZONE, CHARGING METALLIC MAGNESIUM INTO SAID ZONE, HEATING TO MELT SAID SALT AND SAID METALLIC MAGNESIUM THEREBY FORMING MOLTEN METALLIC MAGNESIUM FLOATING ON THE SURFACE OF MOLTEN SALT IN SAID SUMP, INSTILLING ON TOP OF SAID MOLTEN METALLIC MAGNESIUM BETWEEN 60% AND 80% OF THE TITANIUM TETRACHLORIDE THEORETICALLY REQUIRED TO REACT WITH SAID METALLIC MAGNESIUM TO PRODUCE TITANIUM METAL IN THE FORM OF SPONGE IN SAID REACTION ZONE ABOVE SAID SUMP, AND SUBSEQUENTLY FORCEFULLY INTRODUCING THROUGH THE MOLTEN SALT IN SAID SUMP ADDITIONAL TITANIUM TETRACHLORIDE TO REACT WITH METALLIC MAGNESIUM ENTRAPPED IN SAID SPONGE, BY CONTACT FROM THE UNDERSIDE THEREOF, THE TOTAL AMOUNT OF TITANIUM TETRACHLORIDE ADDED BEING BETWEEN 90% AND 98% OF THAT THEORETICALLY REQUIRED TO REACT WITH SAID CHARGED METALLIC MAGNESIUM TO PRODUCE TITANIUM METAL, MEANWHILE MAINTAINING SAID REACTION ZONE FREE FROM CONTAMINATING GASES. 